PROJECT SUMMARY/ABSTRACT Previous studies in rodents have identified five major cell types that are involved in navigation functions, including head direction (HD), place, grid, border cells, and speed cells. Hippocampal Place (HP) cells are reported to encode the spatial location of the animal during active exploration. However, recent studies using head or body fixed virtual reality environments have reported a reduction in HP spatial tuning and a loss of theta rhythm. We hypothesize that these effects upon HP cell function derive from a conflict between visual- locomotor cues and a lack of appropriate vestibular cues to signal active motion. The current project is designed to directly test the type of vestibular motion information used by HP cells to form and maintain spatial location information. Both real world and virtual reality environments will be used while examining HP cell function using a unique virtual reality system we have built that is mounted onto a rotatory motor embedded in a 6DOF hexapod. Specific Aim 1 will determine if HP cells spatial tuning requires vestibular motion signals congruent to visual-locomotion cues by delivering rotational and linear motion profiles that are slaved to the animal's locomotion in the virtual environment. Specific Aim 2 will determine how vestibular rotational and linear motion signals separately affect HP cell function. We hypothesize that vestibular rotational signals are necessary for HP cell spatial tuning and vestibular linear motion cues are necessary for theta rhythm amplitude and frequency. The project represents a new area of research for our laboratory, thus it is appropriate for an exploratory/development R21 application. Our long-term goal is to understand the how vestibular mechanisms contribute to spatial navigation.